The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.
Electro-refining of metals requires placing an anode made from the crude metal to be refined and a cathode together in a suitable electrolytic bath. Application of a voltage between the anode and the cathode causes the crude metal to oxidize and pure metal ions to go into solution and to migrate electrolytically through the electrolytic bath towards the cathode. The pure metal ions are deposited onto the cathode as a refined metal, usually of very high purity. The majority of the impurities are left behind in the electrolytic bath.
Electro-winning of metals requires placing an anode made from a metal that is different from the metal to be refined and a cathode together in a suitable electrolytic bath. The metal to be refined is added to the electrolytic bath in a soluble form (e.g., prepared from a leaching and solvent extraction process). Application of a voltage between the anode and cathode causes the metal to migrate from the solution and deposit onto the cathode as a refined metal of high purity.
A typical cathode assembly includes a flat deposition plate attached along an upper end to an electrically conductive hanger bar. The hanger bar is in electrical contact with an external power source. Normally, the hanger bar rests on a pair of electrically conductive bus bars that run in parallel along opposite edges of the tank. The hanger bar supports the deposition plate within the electrolytic bath and provides a path for the flow of electricity between the power source and the deposition plate.
After a suitable thickness of refined metal has been deposited onto the surface of the deposition plate, the cathode assembly is removed from the electrolytic bath. In cases where the deposition plate is permanent (e.g., formed from a different metal than the metal to be refined), the refined metal can be recovered by any known stripping techniques. Often, vertical side edges of the deposition plate are covered or protected, so that deposition of copper or other desired metal occurs only on the flat side faces of the deposition plate and around a lower edge thereof.
In some cases, a cathode assembly includes an electrically conductive hanger bar (e.g., copper) coupled together with a permanent deposition plate (e.g., stainless steel). The upper end of the deposition plate is typically inserted into a groove provided along the underside of the hanger bar. The deposition plate is then attached to the hanger bar with a weld. The use of dissimilar metals makes the weld particularly susceptible to galvanic corrosion. This corrosion of this weld may result in a reduction in the conductivity of the assembly and the efficiency of the unit as a whole, and may also contribute to mechanical and structural failure.
Introduction
The following introduction is intended to introduce the reader to this specification but not to define any invention. One or more inventions may reside in a combination or sub-combination of the apparatus elements or method steps described below or in other parts of this document. The inventor does not waive or disclaim his rights to any invention or inventions disclosed in this specification merely by not describing such other invention or inventions in the claims.
In one aspect of the specification, there is provided a cathode comprising an electrically conductive hanger bar and a deposition plate attached along an upper end to the hanger bar to define a joint. The cathode assembly further comprises a protective covering having lateral edges and surrounding the hanger bar and a portion of the upper end of the deposition plate so as to substantially enclose the joint and to leave end portions of the hanger bar exposed outside of the lateral edges of the protective covering. Each end of the protective covering includes a corrosion resistant material positioned to form a substantially continuous seal between the protective covering and the hanger bar, thereby to at least hinder fluid flow into the protective covering. It is possible that, for some applications, it may be sufficient to seal the or close off only one end of the protective covering.
The corrosion resistant material may comprise an O-ring, a resin or a tape.
The corrosion resistant material may be positioned around the hanger bar in abutment with one corresponding lateral edge of the protective covering.
Alternatively, each lateral edge of the protective covering is spaced from the hanger bar to form a cavity therebetween and each corrosion resistant material substantially is positioned in a corresponding cavity.
In one aspect, the deposition plate is attached to the hanger bar by at least one weld. In another aspect, the protective covering is attached to the deposition plate by at least one weld. In yet a further aspect, the deposition plate and protective covering are made of stainless steel and the hanger bar is formed from copper.
In one aspect, at each end of the protective covering, a sleeve positioned around and in abutment with a portion of an outer surface of the protective covering and adjacent the corresponding lateral edge and the corresponding adjacent exposed portion of the hanger bar.
In a further aspect of the specification, a method of manufacturing a cathode assembly is described. The method comprises the steps of providing an electrically conductive hanger bar and fastening an upper end of a deposition plate to the hanger bar to form a joint therebetween. The method further comprises the step of providing a protective covering having lateral edges around the hanger bar and a portion of the upper end of the deposition plate so as to substantially enclose the joint and to leave end portions of the hanger bar exposed. The method further comprises the step of at each end of the protective covering, positioning a corrosion resistant material between one lateral edge of the protective covering and one adjacent exposed end portion of the hanger bar to form a seal.
In one aspect, the method further comprises the step of providing the corrosion resistant material as at least one of: an O-ring; a corrosion resistant resin; and a tape.
In another aspect, the method further comprises:
for the O-ring, sliding the O-ring over the hanger bar until it is in abutment with a corresponding lateral edge of the protective covering;
for the corrosion resistant resin, providing a bead of corrosion resistant resin around the corresponding exposed end portion of the hanger bar against the corresponding lateral edge of the protective covering and permitting the corrosion resistant resin to penetrate between the protective covering and the hanger bar; and
for the tape, wrapping the tape in multiple layers around the lateral edge of the protective covering and the corresponding exposed portion of the hanger bar adjacent the lateral edge.
In yet a further aspect, each lateral edge of the protective covering is spaced from the hanger bar to form a cavity therebetween and the positioning step (d) is performed by fitting the corrosion resistant material into the cavity.
In one aspect of the specification, a method of refining a metal in an electrolytic cell is described. The method comprises the step of providing a tank containing an electrolytic bath, an anode assembly in the electrolytic bath and a cathode assembly as described herein in the electrolytic bath. The method further comprises the steps of providing a power source and electrically connecting the power source to the anode assembly and the cathode assembly to form the electrolytic cell. The method further comprises the step of applying a sufficient amount of current to the electrolytic cell to cause metal ions from the electrolytic bath to be deposited onto a surface of the deposition plate of the cathode assembly.
In one aspect of the specification, an electrolytic cell is described. The electrolytic cell comprises a tank containing an electrolytic bath, an anode assembly contained within the electrolytic bath, and a cathode assembly as described herein within the electrolytic bath. The electrolytic cell further comprises a power source electrically connected to the anode assembly and the cathode assembly to form the electrolytic cell.